text: In a homogeneous mixture of moderator and U, the effective resonance integral is found with a good accuracy by the empirical formula below,
  where N/ is the ratio of moderator and U nuclei in the homogeneous mixture, σ is the [http://Nuclear%20cross%20section microscopic scattering cross section] of the moderator. As can be seen from the formula, the effective resonance integral decreases with increasing U concentration. The more U nuclei in the mixture, the less likely absorption by a single nucleus of the moderating neutrons will take place. The effect of absorption in some U nuclei on absorption in others is called resonance level shielding. It increases with increasing concentration of resonance absorbers.
  As an example, we can calculate the effective resonance integral in a homogeneous natural uranium-graphite mixture with the ratio N/N=215. The scattering cross section of graphite σ=4.7 barns;
  :  барн.